The invention involves a variable valve drive for controlling the load of a positive ignition internal combustion engine. Moreover, the invention preferably involves a fully variable valve drive, which can effectuate a throttle-free load control for the internal combustion engine. Furthermore, this valve drive is installed in a position between one cam of a camshaft and at least one intake valve, where the intake valve adjoins immediately with a valve activation component, with a component designed for transmission, and with an adjustment mechanism designed to exert an influence on the lifting function of the transmission component. In addition, this transmission componentxe2x80x94in a drive-like fashionxe2x80x94is built into position between the cam and the valve activation component, and has a first working surface that is opened up by the cam, as well as a second working surface that acts upon the valve activation component.
The advantages of throttle-free load control, over the sort of load control involving fully variable valve drives, are generally known to those skilled in the art. Through such xe2x80x9cde-throttlization,xe2x80x9d one succeeds in putting a stop to the losses that would otherwise come about due to suctionxe2x80x94over a wide range of load conditions of the internal combustion engine.
Thus, DE 195 09 604 A1 discloses a fully variable finger lever drive, whose transmission component, formed as a further finger lever, can be adjusted from a point off center. The transmission component is opened by torsion leg spring which acts as a lost-motion spring.
Referring to this previously known valve drive it is disadvantageous for it to be built to undesirably high levels, as a result of the upright orientation of its transmission component, with the off-center point lying above. In exactly this cylinder head area, as a general rule, there is hardly any building space still in existence for the accommodation of the aforementioned building components. Consequently, in the event of the worst case scenario, costly modifications would have to be made in the area of the cylinder head cover, extending even into the area of the motor. It is further to be established that, in the process of being opened up and adjusted, the lever goes through a very complex course of movement, that is to be controlled only with great difficulty on the basis of intricate interpretation of a highly technical and mathematical nature.
Very often, with the fully variable systems described in the literature, the point in time at which the intake is shut off is also merely altered, with the simultaneous possibility of variation of a lift of the opened gas exchange valve.
The object of the invention, therefore, is to create a valve drive of the aforementioned type, in connection with which the above-cited disadvantages have been eliminated.
In accordance with the invention, this task is accomplished by the fact that the transmission component is produced in such a way that it possesses two parts, and by the fact that it has one lever with the first working surface, and at least one catch with the second working surface, which catch is attached to the lever, at an end of the lever facing the valve activation component, by a pivot center, as well as adjoins with its second working surface at a contact surface of the valve activation component, whereby each catch has a third working surface for the respective adjustment mechanism, that extends on a side that faces away from the second working surface, which third working surface acts on a contact range of the adjustment mechanism during cam lifting, whose lifting is extended in the direction of the opening of the intake, and in connection with which the contact range is movable relative to the third working surface.
By these means, a valve drive is createdxe2x80x94preferably of the fully variable typexe2x80x94that has a clearly lower height of construction as compared with the valve drive that was referred to in the introductory portion of the description. It is to be established, moreover, that it can be more simply constructed, with a clearly simplified course of movement, with adjustment and cam lifting. Consequently, the height of construction in the cylinder head area is either not increased at all, orxe2x80x94if increasedxe2x80x94only to a minimal extent, so that costly modifications are not necessary in the construction components surrounding the interior combustion engine.
The fact thatxe2x80x94through the way in which the contact range is installed on the adjustment mechanismxe2x80x94this contact range is not moved with the valve lifting constitutes a significant difference from the type forming the current state of the art. The contact range moreover is situated in a completely advantageous manner inside of, as well as underneath, a construction area that is canopied by the lever on the side of the valve. In this manner, a valve drive is created that is highly compact in its mode of construction.
Through the solution proposed by this invention, the duration of the opening of at least one opened up intake valve is amenable to being adjusted in a stepless fashion, and the height of the valve lifting is similarly susceptible to such stepless adjustment. Moreover, with respect to some further systems described in the current state of technology, it is advantageously the case, that even the time period for the opening of the intake can be retarded. In this context, it is suggested that the camshaft be equipped, in a familiar mode of construction, with a device for its relative rotation. In this manner, a backward adjustment that might perhaps be desired in the xe2x80x9cearlyxe2x80x9d direction can also be realized.
In a pivoting movement of the lever in the opening direction of the intake valve, the catch that is positioned for pivoting movement at the one end of the lever travels through a motion channel lying between a contact surface of the valve activation component and a contact range of the adjustment mechanism. In the motion channel, the catch can be forcibly shifted as to its position, as a function of a pivoting movement of the adjustment mechanism in the direction of the opening of the intake valve. This forcible pivoting movement in the aforesaid opening direction, consequently, results in the fully variable opening movement of the intake valve. In the zero lifting section, the catch merely rotates around the pivot center of the lever.
It is especially advantageous, in accordance with the invention, when for reasons of symmetry, one catch is installed on each of the two sides of the lever. Each of these catches then works with at least one gas exchange valve indirectly over each one of the finger levers. In a further development of this embodiment, the contact ranges of the two catches can be endowed with different lifting characteristics. This design can be utilized for the formation of a mixture-forming spin effect in the combustion chamber.
In an advantageous manner, the adjustment mechanism is adjoined directly to the lever and proceeds in a further advanced development of the invention, in accordance with which, the lever is formed as a rocker arm on the axis. It is also conceivable, however, that the adjustment mechanism might be formed as a construction component that is entirely removed and separated from the lever, which construction component can also have geometrical proportions that deviate from the finger form. It is only important that the adjustment mechanism should produce an adjustable pivoting movement for the catch in the direction of the opening of the intake valve.
In an advantageous manner, the zero lifting section of the contact range of the adjustment mechanism is formed with a sufficient length, that by the corresponding positioning of the catch to this area, either a zero lifting, or only a minimal lifting is produced at the intake valve. Consequently, the entire system can also be utilized for purposes of shutting off the valve, as well as for cylinder shut-off.
A highest valve lifting is produced at the intake valve, when the adjustment mechanism is rotated with reference to the third working surface of the catch, in a manner such that the third working surfacexe2x80x94by cam liftingxe2x80x94travels through a maximum increase of the contact range of the adjustment mechanism. At the most remote point, this maximum increase lies at the beginning of the zero lifting section, which beginning is located on the side of the lever. An adjustment can be effectuated during the entire course of a cam run.
In the event that this becomes necessary, the lever can be withdrawn entirely with the opening up of the cam. It is only important in this case that the catch should experience the forced spatial movement, within the motion channel, for example, through a crank drive, or the like.
It is, moreover, a preferred feature of the invention, that the valve activation component can be produced as a finger lever. With that which is implied by the scope of protection of the invention there are also valve activation components, that, for example, may be produced as either finger levers or rocker arms, but also as a tappet. Furthermore, the variable valve drive that has been suggested can also be applied in the case of a tappet drive.
In order to achieve a permanent position of the lever at the cam, the lever is acted on by means of a lost-motion element, such as a helical spring in the direction of the cam. This spring mechanism can also be installed in an advantageous manner in the construction space that is canopied by the lever on the side on which the valve is located. In addition, it is particularly advantageous that the length of this spring is not concomitantly adjusted in conformity with the lifting adjustment, contrary to what was said of the current state of technology as referenced in the introductory portion of this description. In that case, an undesirable relaxation of this spring is brought about, in the direction of a smaller lifting, as a result of an associated adjustment.